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DC-DC Converter Makes Single-Cell Microcontroller

Silicon Labs has met the
challenge of cutting
power consumption
to a single cell with its
C8051F9xx, which fits into a 4- by
4-mm package (Fig. 1). Ranging
from 0.9 to 3.6 V, its operating
voltage is ideal for one- or twocell
solutions.

This 25 MIPS, 8051-compatible
microcontroller has a 5-V tolerant
I/O with a built-in 24.5-MHz (2%
accuracy) clock. It also boasts a
second, low-power 20-MHz clock
and a 32-bit SmaRTClock timer
in addition to multiple 16-bit timers
with pulse-width modulation
(PWM) support.

The key is a dc-dc converter
and low-dropout (LDO) voltage
regulator that was designed specifically
for the chip, allowing it to
operate with efficiency between
75% and 90%. It supplies a
constant 1.7 V to the core, and it
can even deliver up to 65 mW to
the chip and external devices. In
sleep mode, the chip draws less
than 50 nA.

Typical off-chip dc-dc converters
cannot match this performance and efficiency across the range of voltages and
current requirements. They usually provide more flexibility in output voltages as well as
other features. However, they aren’t as relevant to a single-chip solution such as the
C8051F9xx. For example, higher current would be overkill. Likewise, the C8051F9xx is
an extremely tiny single-chip solution.

Silicon Labs’ tests show the C8051F9xx running twice as long as the competition in
two-cell trials. Likewise, the chip can work with a
range of battery technologies, from nickel metal hydride (NiMH) to zinc air in addition
to
traditional alkaline and lithium-ion (Li-ion) batteries.

The chip’s low-voltage operation provides other power advantages. For instance, a
single AA has more power than a pair of AAA batteries, but it takes up about the same
space. Similarly, migrating from a single AAA to a single AA increases battery life by 2.2
times. A power simulation application enables designers to estimate requirements early
in
a design (Fig. 2).

Silicon Labs didn’t skimp on the peripherals and memory. The chips have 64 kbytes
of
flash and 4352 bytes of RAM. A pair of comparators can handle up to 15 capacitive
touch inputs and a 10-bit, 15-channel, burst-mode, 300-ksample/s analog-to-digital
converter (ADC) with an internal voltage reference, allowing extremely fast wakeup/
record times from sleep mode. Digital peripherals include a UART, an SMBus interface,
and a pair of master/slave serial peripheral interface (SPI) ports.

Pricing starts at $1.99. A $99 development board and low-cost ToolStick daughter
cards that start at $18 are available (see “Silicon Labs Does It Again With New ToolStick”
at www.electronicdesign.com, ED
Online 14025).

Sandia National Laboratories
is building a
prototype that will use
concentrated solar power
to chemically “reenergize”
carbon dioxide into
carbon monoxide, which
then could be used to
make hydrogen or serve
as a building block for
synthesizing liquid combustible
fuel like methanol
or even gasoline and
diesel. Known as the
Counter Rotating Ring
Reactor Recuperator
(CR5), the device should
be complete by early next
year. Tests breaking water
down into hydrogen and
oxygen are already under
way, and researchers
expect commercialization
in 15 to 20 years. See associated figure